Fix callback deadlocks after calling mosquitto_disconnect(), when using the threaded interfaces. Closes bug #1313725.

Thanks to Michael Frommberger.

ChangeLog.txt

@@ -18,6 +18,8 @@ Broker:
 
 Client library:
 - Fix topic matching edge case.
+- Fix callback deadlocks after calling mosquitto_disconnect(), when using the
+  threaded interfaces. Closes bug #1313725.
 
 General:
 - Use $(STRIP) for stripping binaries when installing, to allow easier cross

lib/net_mosq.c

@@ -776,6 +776,7 @@ int _mosquitto_packet_write(struct mosquitto *mosq)
 				mosq->on_disconnect(mosq, mosq->userdata, 0);
 				mosq->in_callback = false;
 			}
+			pthread_mutex_unlock(&mosq->callback_mutex);
 			pthread_mutex_unlock(&mosq->current_out_packet_mutex);
 			return MOSQ_ERR_SUCCESS;
 		}